Ultrathin Co/Pt and Co/Pd superlattice films for MgO-based perpendicular magnetic tunnel junctions

Abstract

Ultrathin [Co/Pt]n and [Co/Pd]n superlattice films consisting of 0.14–0.20-nm-thick Co and Pt(Pd) layers were deposited by sputtering. A large perpendicular magnetic anisotropy [(3–9)×106 ergs/cm3] and an ideal square out-of-plane hysteresis loop were attained even for ultrathin superlattice films with a total thickness of 1.2–2.4 nm. The films were stable against annealing up to 370 °C. MgO-based perpendicular magnetic tunnel junctions with this superlattice layer as the free layer showed a relatively high magnetoresistance ratio (62%) and an ultralow resistance-area product (3.9 Ω μm2) at room temperature. The use of these films will enable the development of gigabit-scale nonvolatile memory.

Correlation between Pd metal thickness and thermally stable perpendicular magnetic anisotropy features in [Co/Pd]n multilayers at annealing temperatures up to 500 °C

“…Thus, since it is widely believed that the Co/Pd intermixing or Pd diffusion is one of the main factors for PMA degradation during annealing process, 16 Co and Pd thicknesses were frequently used in the MLs. 4,14,16 Therefore, more detailed studies are necessary to clarify the structural characteristics in ML configurations.…”

“…[5][6][7][8] Among them, artificial ML matrices composed of ferromagnetic and noble metals, such as Co/Pd, Co/Pt, Fe/Pd, and Fe/Pt, have shown that ML matrices are promising candidates for use in p-MTJs. 4,[9][10][11][12] Alternating two ultra-thin layers with different thicknesses in the ML matrix permits appreciable tuning of magnetic characteristics and yields strong PMA features. These PMA properties may originate from possible interface spin-orbit coupling between ferromagnetic/noble metals.…”

“…Here, E = K eff V is the energy barrier, M S is the saturation magnetization, H k is the anisotropy field, K eff is the effective perpendicular magnetic anisotropy (PMA) energy density, V is the volume of the magnetic layer, k B is the Boltzmann constant, and T is temperature. 3,4 In particular, a perpendicular magnetic tunnel junction (p-MTJ) suitable for PMA characteristics is a key factor to obtain a low J C and a high thermal stability, which cannot be achieved with in-plane MTJ (i-MTJ). 3 A variety of PMA systems including an L1 0 alloy, multilayers (MLs), and rare earth-transition metal (RE-TM) alloys have been extensively employed to yield outstanding PMA performance.…”

Engineering spin-orbit torque in Co/Pt multilayers with perpendicular magnetic anisotropy

“…In this work, we would like to evaluate the SOT in the Co/Pt multilayers (MLs), which possesses good enough PMA with tunable volume of the FM layer and also shows a good magnetoresistance in MgO-based 3 magnetic tunnel junctions with the interfacial CoFeB insertion. 14,15 Although a high SOT has been reported on the Co/Pd MLs recently, 13 no systematic works have been done for explaining the presence of SOT in the multilayers, where the spin currents from heavy metal may counteract each other and no Rashba interaction can be seen without structure inversion asymmetry. By conducting the lock-in technique, [16][17][18] the dependence of SOT efficiencies of the Co/Pt MLs on different repeating layer number (N) is investigated.…”

Atomic-Layer Alignment Tuning for Giant Perpendicular Magnetocrystalline Anisotropy of3dTransition-Metal Thin Films

“…Pd) elements, [3][4][5][6][7][8][9] which exhibit large PMA that promisingly overcomes the shape in-plane magnetic anisotropy and thermal fluctuations on a device level.…”